Amyloid-beta (A-beta), which exists as a 36-43 amino acid peptide, is a product released from amyloid precursor protein (APP) by the enzymes β and γ secretase. In AD patients, A-beta can be present in soluble monomers, insoluble fibrils and soluble oligomers. In monomer form, A-beta exists as a predominantly unstructured polypeptide chain. In fibril form, A-beta can aggregate into distinct morphologies, often referred to as strains. Several of these structures have been determined by solid-state NMR.
For, example, structures for several stains of fibrils are available in the Protein Data Bank (PDB), a crystallographic database of atomic resolution three dimensional structural data, including a 3-fold symmetric Aβ structure (PDB entry, 2M4J); a two-fold symmetric structure of Aβ-40 monomers (PDB entry 2LMN), and a single-chain, parallel in-register structure of Aβ-42 monomers (PDB entry 2MXU).
The structure of 2M4J is reported in J. X. LU, W. QIANG, W. M. YAU, C. D. SCHWIETERS, S. C. MEREDITH, R. TYCKO, MOLECULAR STRUCTURE OF BETA-AMYLOID FIBRILS IN ALZHEIMER'S DISEASE BRAIN TISSUE. CELL Vol. 154 p. 1257 (2013) and the structure of 2MXU is reported in Y. XIAO, B. MA, D. MCELHENY, S. PARTHASARATHY, F. LONG, M. HOSHI, R. NUSSINOV, Y. ISHII A BETA (1-42) FIBRIL STRUCTURE ILLUMINATES SELF-RECOGNITION AND REPLICATION OF AMYLOID IN ALZHEIMER'S DISEASE. NAT. STRUCT. MOL. BIOL. Vol. 22 p. 499 (2015).
A-beta oligomers have been shown to kill cell lines and neurons in culture and block a critical synaptic activity that subserves memory, referred to as long term potentiation (LTP), in slice cultures and living animals.
The structure of the oligomer has not been determined to date. Moreover, NMR and other evidence indicates that the oligomer exists not in a single well-defined structure, but in a conformationally-plastic, malleable structural ensemble with limited regularity. Moreover, the concentration of toxic oligomer species is far below either that of the monomer or fibril (estimates vary but on the order of 1000-fold below or more), making this target elusive.
U.S. Pat. Nos. 5,766,846; 5,837,672; and 5,593,846 (which are incorporated herein by reference) describe the production of murine monoclonal antibodies to the central domain of the Aβ peptide. WO 01/62801 describes antibodies that bind A-beta between amino acids 13-28. WO2004071408 discloses humanized antibodies. WO2008088983A1 describes an antibody fragment that binds amyloid beta (A-beta) peptide and is covalently attached to one or more molecules of polyethylene glycol (PEG), the antibody fragment specifically binding human A-beta peptide between amino acid positions 13-28. Solanezumab and Crenezumab bind amino acids 16-26 on A-beta. Crenezumab interacts with the monomer, oligomer and fibril. Midregion antibodies, including solanezumab (picomolar affinity) and crenezumab (nanomolar affinity), appear to preferentially bind monomeric A-beta [1].
Antibodies that preferentially or selectively bind A-beta oligomers are desirable.